1. Field of the Invention
This invention relates to a stripping foil preferably usable for a charged particle accelerator, and a method and an apparatus for fabricating the stripping foil.
2. Description of the Prior Art
Conventionally, a stripping foil has been employed to extract from a negative ion beam introduced from an external ion source. With the stripping foil, an electron of the ion beam is scattered and ionized by the coulomb force from an atomic nucleus of the substance constituting the stripping foil, and thus, a desired charged particle such as a proton can be injected while the ion beam is penetrated through the stripping foil.
FIG. 1 is a schematic view showing a charged particle accelerator including a stripping foil, and FIG. 2 is a structural view showing the stripping foil. As is shown in FIG. 1, a negative ion beam is penetrated through a stripping foil to be converted into a given positive charged particle, which is introduced into a charged particle accelerator. Then, the charged particle interflows with another charged particle introduced previously and is accelerated with circulating orbit. On the other hand, as shown in FIG. 2, the stripping foil is formed very thin in a rectangular shape, so that it is required that the three side edges of the stripping foil without the side edge exposing to the circulating orbit are supported in order to maintain the stripping foil stably.
At present, in order to increase the number of charged particles to be accelerated in a charged particle accelerator, a phase space painting to introduce the charged particles dispersed vertically and laterally in a given degree has been planned. In this case, a large amount of charged particles are introduced and penetrated through the same stripping foil, the stripping foil may be deformed and damaged by excess heating or the like.
In this point of view, in order to decrease the number of charged particles to be introduced into the same stripping foil, such an attempt is made as to reduce the size of the stripping foil almost equal to the diameter of the charged particle or to change and shift the circulating orbits of the charged particles with a pulsed electromagnet.
With the stripping foil of which the three side edges are supported as shown in FIG. 2, all of the charged particles circulating their respective orbits are introduced into and penetrated through the stripping foil, so that the above-mentioned problems are posed on the stripping foil. In this point view, various stripping foil-supporting structure are proposed. Concretely, as shown in FIG. 3 is proposed a supporting structure where the two side edges of a stripping foil are supported, and as shown in FIG. 4, is proposed a supporting structure where a stripping foil is supported by thin wire set up vertically from a supporting frame.
With the corner foil structure shown in FIG. 3, the number of charged particles can be reduced almost half, compared with the three side edge supporting structure shown in FIG. 2. However, since the circulating orbits of the charged particles are always set on the stripping foil, the number of the charged particles are not reduced per unit area of the stripping foil. As a result, with the corner foil structure, the stripping foil is deformed and damaged in the same degree as with the three side edge supporting structure. With the wire supporting structure as shown in FIG. 4, since the wire are located in the circulating orbits of the charged particles, the charged particles are scattered by the wire, resulting in the damage of the wire.